Which kind of UVs are being used?
They are normal UV's, although a UDIM style layout has been used. UDIM support in blender is being worked on and should be included in the 2.80 release.

UDIM support will allow a single material to use multiple image textures, all sharing a single UV layout.

The model you have uses multiple materials, each assigned to a different part of the mesh. Each material uses the same UV layout with a different image texture. In the end the result is the same.

This is possible from the way UVs work, the position of a vertex in the UV layout is an X,Y position on the image as a percentage, that is a range from zero to one, so 0.0 is one side of the image, 0.5 is the middle and 1.0 is the other side. This helps by allowing us to use different resolution textures with the same UV layout. Unless set to clip, an image texture will repeat continuously, so a UV position of 1.5 resolves to the same image location as 0.5. In this case it is only used for clarity, you will get the same result by placing each section directly on top of each other.

The main difference with UDIM is that it repeats on larger numbers, were UVs go from zero to one, a UDIM layout can be zero to ten, with each whole number corresponding to a different image, so 1.5 will be the middle of the second image, 3.5 the middle of the fourth and 10.5 should wrap back to the same place as 0.5 on the first image.

For reference ptex is another approach to this from Disney, it allows a different texture resolution to be used for each polygon, technically it is considered a different texture for each face and doesn't use UVs, all thee textures are then combined into one texture file. There has been some work done to add ptex to blender but it has never been completed.